Electronic Arts has purchased Facebook games developer Playfish for USD$400 million.

The company, the second most popular Facebook games developer after Zynga, was expected to reach USD$75 million in revenues this year. These revenues are generated by traditional advertisers as well as sponsors who agree to buy in-game upgrades for users who try their products. They also monetise via players who make micro-payments to progress more quickly.

Industry leader Zynga reportedly turned over USD$250 million in 2009.

Although hard data is unavailable, industry commentator consensus is, currently, the major revenue source is in-game purchases rather than advertising. For example, Valentines Day saw Playfish sell four million virtual flowers from USD5c to USD$2.

For aficionados, Playfish games include Country Story, Pet Society and Restaurant City.